In a plate-type safety ski binding each of the skiboots is fitted with a plate that in turn is secured at its front or toe end and heel or rear end on the upper surface of the ski. A spring-loaded pressing pin which can swivel in several directions pushes this plate against an abutment. If a plate is twisted or tipped with a force exceeding a predetermined level the pressure pin will swivel and release the plate from the ski.
Some such bindings have complicated devices both at toe and heel of the ski. These are separately adjusted for various kinds of release action. Such bindings are relatively expensive and frequently very hard to adjust. Furthermore it is often a relatively tricky procedure to fit the skiboot carrying the plate into the binding.
In a particular type of plate binding a circular pivot disk is used instead of the pressure pin. This disk engages in a longitudinal slot approximately in the center of the boot-mounted plate. Thus this plate is pivotal about the axis of the disk and simultaneously is displaceable to a limited extent longitudinally of the ski. The rear end of the plate has a beveled abutment surface which is circularly arcuate and centered on the axis of the disk and which lies on a corresponding surface of the ski-mounted binding. A spring-loaded locking pin engages the plate and presses it against the abutment surface. The plate and therefore the boot can be turned sideways. In case of a fall forward the plate can also spring out of the holder against the force of the spring.
In practice it has been found that the force needed to return a slightly twisted plate back to its centered position is considerably too great. In theory the force of the pivot pin should be taken up by the pivot disk until the two abutment surfaces fit tightly within one another. The spring force of the pivotal pin cannot be adjusted to achieve this effect except when the plate is slid forward in falling. The plate can however be pulled off the ski if it is pushed forward with considerable force, as for example when the skier passes over something that brakes his ski.